Electric tube construction



Feb. 1, 1938. c. A. HORN ELECTRIC TUBE CONSTRUCTION l Sheets-Sheet l Filed Dec. l1, 1935 INVENTOR [MPM/cf AHM/v BY Y 5 M man@ ATTORNEYS Feb. 1, 1938. c. A. HoRN ELECTRIC TUBE CONSTRUCTION Filed Dec. ll, N35 4 Sheets-Sham'I 2 IN V E N TO R Afm/cf A Ha/v l ATTORNEYS Feb. 1, 1938.A c. A. HORN 2,107,254

ELECTRIC TUBE CONSTRUCTION Filed DeC. 1l, 1935 4 SheelLS-SheekI 3 INVENTOR CM/PfA/cf A Ha/v BY ,6m/am MM ,f ,Qu/@V ATTORNEYS Feb. 1, 1938. C, A HORN 2,107,254

ELECTRIC TUBE CONSTRUCTION Filed Dec. 1l, 1935 4 Sheets-Sheet 4 B Y @mm mut/f pm ATTORNEYS Patented VFel. 1, 1938 UNITED STATES 2,101,254 ELECTRIC TUBE CONSTRUCTION Cla-.rence A. Horn, Roselle Park, N. J., assigner to Arcturus 'Development Company, Newark, N. J., a corporation' of Delaware Application December 11, 1935, Serial No. 53,848

24 Claims.

10 elements lwithin the envelope upon a so-called stem. This stem consists of a tubular member having a base flare sealed to the base of the envelope and having an upper or inner press in which the various lead-in wires are sealed. The press of this stern in the prior art is formed by a lateral compression of the stem wall edge which forces the material together to form a flattened mass in which the glass coalesces and seals the envelope interior so that a vacuum may be formed, if desired, within the envelope.

A difficulty of the type of construction as above described has been the inability to diminish the length of the stem to a point where small size tubes could be manufactured. In recent years, particularly in the radio art, it has become highly desirable to utilize tubes of short length so that the installation in a radio set would occupy a. minimum of space. Such requirements arise from use of radio sets in a number of ways where the amount Of space allowed is limited.

been the limitation of the stem press available for support of lead-in wires and the like, requiring crowding of the wires and resultant losses due to leakage and increased capacity and inductive effects.

It is accordingly an important object of the present invention to provide an electric tube in which the length of the stem may be diminished to an over--all length of less than one inch, and which may be successfully manufactured in lengths of approximately one-half inch or less for the standard radio' tube.

Another object of the invention is to provide a type of stem assembly for an electric tube wherein the distance between the lead-in and support wires may be increased over that in the Ordinary glass vacuum tube.

Another object of the invention is to provide a stem assembly for radio tubes in which a material reduction is effected in the capacity, resistance and inductance of the lead-in wires.

An object of the invention also is to provide a stem assembly including a plurality of lead-in wires concentrically arranged whereby a maxi- A further difficulty in the prior art tubes has (Cl. Z50-27.5)

mum length of stem mass is made available for wire support.

l Still another object of the invention is, to provide a stern construction for an electric tube in which the blow-out aperture to the tube interior is along the tube axis.

` Another object of the invention is to provide means for decreasing electrolysis within the envelope of an electronic device between the various lead-in wires.

Additional objects pertain to a tube construction wherein tube operating temperatures are lessened, inter-element capacities are made more uniform, and the possibility of shorts between wires and ground is-diminished.

Further Objects of the invention will be apparent on consideration of the forms of the invention which may be preferred as hereinafter described and as shown in the accompanying drawings, in which:

Fig. 1 is a view of the stem assembly unit;

Fig. 2 is a view of the tube lead-in Wire prior to the heat treatment in the tube manufacture;

Fig. 3 is a View of the 'exhaust tube used in the tube manufacture;

Fig. 4 is a view of the stem employed;

Fig. 5 is an elevation partly in section of the rotatable head of the stem making machine;

Fig. 6 is a section along lines 6-6 of Fig. 5;

Fig. '7 is a section along lines 1-1 of Fig. 5;

Figs. 8, 9, 10 and 11 are views of the stem unit in process of construction;

Fig. 12 is a section along lines l2-I2 of Fig. 11;

Fig. 13 is an elevation partly in section of the stem unit with the various electrode elements of a radio tube attached thereto;

Fig. 14 is a modification of the invention showing the short stem construction;

Fig. 15 is a view of the preheater apparatus;

Figs. 16 'and 17 are views of a radio tube showing steps in the sealing cf theenvelope;

Figs. 18, 19 and 20 are views of modifications of the invention;

Figs. 21, 22, 23 and 24 are views of a modification in which the use of beads are eliminated;

Figs. 25 and 26 are modications employing a stem of large diameter;

Fig. 27 is a further modification;

of Fig. 27;

Fig. 29 is a view oi.' a radio tube embodying my invention; and

Fig. 30 is a sectional view through said radio tube along lines 32-32 of Fig. 29.

In the description the term electric tu is Fig. 28 is a sectional view along lines 30-30 employed as a generic term covering devices such as radio'tubes, electric lamps, X-ray tubes and the like employing a sealed envelope.

Generally speaking, the invention oi the present application comprises a tube construction utilizing a new type glass stem which will permit of lengths as low as one-quarter inch. The essential features of the stem construction or unit include a tubular stem having one end bridged by a mass of glass added to the stem glass to form an end wall, said wall holding the various lead-in and support wires, as well as the exhaust tube which connects with an aperture formed in the wall.

In the form oi the invention which will nowY be described, use is made of a plurality of globules or beads oi glass positioned in a common plane at the inner end of the stem, these beads on heating coalescing one with another and with the end of the stem to form a gas-tight seal across the stem end. The invention will be described as applied, for illustrative purposes, to a radio tube, Fig. l illustrating a stem unit of this type.

In Fig. 2 is shown a lead-in wire III for use in a radio tube. This wire is of the usual copper covered construction, and adjacent one end a bead of glass II is sealed to the copper-coated wire through a thin lm oi copper borate, thus insuring with the copper coat a tight seal through various changes of temperatures.

In Fig. 3 I have illustrated the exhaust tube I2 used in the assembly of the stem unit, and in Fig. 4 the stem I3 is illustrated showing the flared end I4 which connects with the open end of the tube envelope.

Use is made of the usual rotating head'stem making machine in use for many years in electric lamp and radio tube manufacture, such as the Eisler machine. In this machine there are a plurality of rotatable heads which are mounted on the periphery of a rotatable frame or plate, each head for different positions around the axis being subjected to a different heat treatment, and at stated points being subjected to certain mechanical operations such as the positioning of the lower end of the exhaust tube I2 (Fig. 8), the press operation on the stem (Fig. l0) and the blow-out operation to provide an aperture for the exhaust (Fig. 11) This type machine as adapted for the present invention utilizes a head such as that shown in Fig. 5 of the drawings partly in section, and generally indicated by the numeral 8. To the base I5 of the rotating frame oi the stem making machine is secured the rotatable member 3 on which is mounted the two uprights I8 and I `I which are united in a head I8 having a hollow center, and in this hollow center a plunger 20 is adapted to have axial movement. The plunger is adjustable by the screw thread connection 2I and is movable through the base connection 22, there being appropriate cam elements operable at stated points in the rotation of the stem making machine to operate the plunger.

Pivotally attached to the uprights IS and II are clamp members 23 and 24 having at their upper ends inwardly projecting lugs 25 and 26 to which are attached the jaws 2l and 28 for holding the flared end of the stem. As shown, these jaws are approximately semi-circular in form and are provided with annular grooves 29 and 30 on the cooperating edges of the jaws 21 and 28, in which grooves the curvededge of the flange seats during the stem unit forming operation. A spring 3I connecting the upper sections of the clamp members 23 and 24 is provided lor normally returning the jaws of the clamp in closed position. The fixture 9, which is removable in the head I8 of the rotatable unit I, is provided, as shown in Figs. 5 and 7, with a series of recesses 32 and 33, the recesses 32 being adapted to receive the short end of the lead-in wires below the bead and the recesses 33 to receive the bent end of the support wires 34, as shown in Fig. 1, the other end of these wires being free. Use is made of the projecting pins 35 on opposite sides of the top of the fixture 9 to hold the support wires 34 in position during the stem making operation. As illustrated in Fig. 5, the

various lead-in and support wires form, in this.

In the area internal to the beads I I is inserted:

the exhaust tube I2, the lower end of which rests on the top of the plunger 20. As means for holding the exhaust tube in position during the manufacturing operation I have provided a set of jaws 8| and 82 controlled by appropriate mechanism to retain the tube I2 in position. This mechanism includes a rotatable shaft 83 provided with an operating handle 8l at its base and mounted in a tubular member 85 secured to `the rotatable head I8 by means of the lug 86, the collars 81 and 88 attached to the rotatable shaft providing a limitation for axial movement of the shaft. Formed in the collar 88 is a yieldable locking member 89 which is adapted to have vertical movement into engagement with the angularly displaced recesses 90 formed on the base of the lug 88, by which means the rotatable shaft is yieldably held at either limit of its movement. The rotatable shaft 83 extends above the head of the rotatable unit l and terminates in an arm 9| which is xedly attached thereto. This arm is provided with a link 82 pivotally attached thereto and to a jaw 82, the end of which normally is adapted to engage the upper end of the exhaust tube I2. Positioned on the rotatable shaft 83 directly beneath the arm SI so as to have limited rotation thereon, is a second arm 94 which extends toward the jaw 82 and terminates in a cooperating jaw 8I which is adapted to coact with the jaw 82 for holding the exhaust tube in position. 'I'he arm 34 carries a pin 95 forming a stop, providing a lost motion between the arm SI and the stop. The plvotal pin between the link 92 and the jaw 82 is provided with a spring 98, which spring urges the jaw 82 in the direction of the exhaust tube I2. The outer end of the arm 94 is bifurcated, forming two extensions between which the jaw 82 is guided. At the base of the rotatable shaft 83 is a coil spring 91, one end of which is fastened to the handle 84 and the other end to the xed pin on the member I8, this spring normally urging the clamping means in a clockwise direction looking down at the top of the apparatus.

In operation, with the jaws in open position displaced from the axis of the head of the apparatus, the handle is turned to release the yieldable locking member 89 and the tension of the spring 91 forces the arm 94 in a clockwise position until the jaw 8I reaches the inner limit of its movement. The exhaust tube I2 is then placed in position in the head and the cooperating jaw 82 brought into engagement with the plete radio tube include a preheating operation. as indicated diagrammatically in Fig. 15 of the tnbe, thus holding it ilxediy in position ready for the various sealing operations. Y

With the Various leadin wires with their attached beads and the exhaust tube and stem positioned as Ashown in Fig. 6, the machine rotates the table carrying the unit 8 to its next position wherein the plunger 20 is elevated tb bring the' base of the exhaust tube to the level of the various beads at the open end o1' the stem I3, as shown in Fig. 8 of the drawings. In this position, also, moderate heat is applied from gas jets, for example, two jets on either side of the stem, the mechanism during this time rotating the stem unit. l

At the next position increased heat is applied, as for example five gas jets on either side of the' head unit 8; the plunger 20 has been lowered; the base of the exhaust tube I2 has softened, assuming a somewhat globular formation; and the various beads -II are fusing to the lower edge of the stem I3, as shown in Fig. 9. In the next position, as shown in Fig. 10, where a heat of approximately twelve jets is applied to the stem, the fusion progresses to a point where a globule of glass on the exhaust tube l2 has been formed and constriction and shrinkage of the wall glass has taken place, reducing the opening in the lower or beaded end of the stem so that when the plunger 20 is again moved upwardly by cam action and the lever 43 is moved downwardly by,` cam action there is brought about a bridging of the end'of the stem through the partial fusion of the beads and the button formed on the end of the exhaust tube I2. In this position the lower plunger 20 moves to ar point above the plane of the stern end to bring about a slight compression of the softened glass and to form a depression'l in the wall, movement of the exhaust tube upwardly being prevented by a simultaneous action of the lever 43 provided with a compression head 44 adapted to engage f the top end of the exhaust tube. This movement of the lever 43 also forces down the exhaust tube I2 where melting of the lower end of the exhaust tube has withdrawn the lower end from contact with the glass mass in the stem. In the next and nal position of the sealing mechanism, as shown in Fig. 11, a reduced heat of approximately six gas jets is applied while simultaneously air pressure from the nozzle 45 is introduced in the upper end of the exhaust tube I2, causing a blowing out at the molten base of the glass wall 6, forming a hollowed projection 46 surrounded by an annular recess 41 in the depression 1. This completes the manufacture of the stem unit 5 which is in the form of Fig. l, and is now ready for connection to the various electric elements of the tube assembly.

The `stern unit as above described is provided with a flare at one end with appreciable depth. It is, of course, obvious that a stem of less depth could be employed, such as shown for example in Fig. 14. where the length of the stem is practically that of the glass wall 48 closing the open end of the stem.

'Ihe stem unit 5 as completed in accordance with the above process may now be applied to various electrical elements such as those of a radio tube construction. In Fig. 13 the stem unit is shown so applied, the electrical element assembly 49 being connected to the various lead-in and support wires of the stem unit to form a combined stem and electrical element assembly 4. A mica disc 50 forms a convenient insulating support between the two units.

Further steps in the processof making the comdrawings, wherein these various stem units are inserted on a moving support and pass through an oven. Preferably an annular movement is found more practical than the diagrammatic linear movement shown. In this preheating operation the strains as between the thicker beads and .the thinner glass web joining the beads are released and the temperature. of the unit is brought up tc a point where they may be readily applied to the heated envelope sealing machine without danger of fracture through rapid heat changes.

An individual head unit of the envelope sealing machine is illustrated in Fig. 16 of the drawings. As shown, this unit includes the hollow and rotatable supportvmember 5I having annular ridges 52 and 53, the ridge 53 being provided with an inclined surface 54 for'a purpose to be hereinafter described. The upper end of the support '5I is slightly ared outwardly and is adapted to contact with and support the flare I4 of the stem I3, the exhaust tube and the exposed lead-in wires projecting into the hollow interior of the support 5|. A cylindrical glass envelope 55 is applied over the stem and electrical assembly unit and heat is applied at the points indicated by arrow adjacent the flared edge of the stem at one position of the movement of the head unit on the rotating frame of the machine. This brings about a softening of the glass at this point, causing a gradual constriction of the glass toward the stem until contact is made with the flared edge and fusion therewith is brought about. constriction is aided by the pressure of the gas flame directed toward the axis of the rotating head unit. In a subsequent position the gas flames are directed to a point below the ared edge, the heat being of suilicient intensity to cause melting of theglass. and the weight of the skirt of the glass envelope 55 brings about a separation at the flared edge. the glass skirt falling down onto the inclined surface 54 of the annular ridge 52, there to be removed or broken by the operator. The envelope is now ready for evacuation, which takes place through the exhaust tube I2, after which operation the exhaust tube is 'sealed ofi", as shown in Fig. 30, and connected to the tube base.

The externally extendingl lead-in wires are connected to the various external terminals (Fig. 30) in the base plate 6I. A yielding, corrugated metal strip 62 is placed about the upper end of the envelope 55, and a metal can B3 inverted over the envelope 55 and secured to the base 6I by any appropriate means, such as the turning in of the edge at various points of the can periphery, as shown at 64. The sealed-off section of the exhaust tube is enclosed in a central depending insulation cup 55 which is adapted for insertion in a centering aperture of the socket, as is well known in this art. f

In the above embodiment of my invention I have described a construction in which a plurality of beads or globules of glass are employed to form the closing wall of the stem in conjunction with the straight end of the exhaust tube. It is apparent that variations from this specific illustrative example may readily be mad-e. In Fig. 18 I have shown a modification in which the exhaust tube is terminated by a at button 66, the tolerance as between the periphery of the button and the various beads II being negligible in value. This construction makes possible the elimination This 19 a further modification is shown in which there is a limited tolerance between the button Bland the beads, this construction-requiring, however, the use of the upper lever I3 to force the exhaust tube end into position in the glass wall. The modification of Fig. 20 is somewhat similar to that of Fig. 19 except largertolerances are employed requiring use of the upper lever I3 and lower plunger 20 in securing the final conformation of the sealing wall of the stem.

Figs. 21 to 24 illustrate a modification of the invention in which the use of beads is eliminated. As previously explained, it is apparent that the use of beads adds body for the formation of the wall. However, it is possible for certain uses to employ the bare wires 68 in conjunction with the exhaust tube I2 and the stem i3. In this arrangement in Fig. 21 is illustrated the original conformation of the various stem elements with gas flames adapted to be directed against the lower stem edge; Fig. 22 illustrates the incipient fusion of the lower stem edge and the lower end of the exhaust tube; Fig. 23 illustrates the combination of these fused elements and the upward movement of the plunger 20 together with the downward movement of the lever 43 to form the central depression G9; and Fig. 24 shows the completed stern with the exhaust tube aperture blown out at the base through the depression 69. It is noted that the combination of the stem and exhaust tube is aided by the slight pressure of the gas flame jets.

In Figs. 25 and 26 are illustrated modifications wherein a stem of increased size is employed. In the arrangement of Fig. 25 an enlarged exhaust tube 10 is utilized to supply the added glass for the base wall, this tube 10 being formed, however, with a constriction 1i at the sealing-off point to facilitate the sealing operation of the exhaust tube. The modification of Fig. 26 utilizes the button 12 at the base of the exhaust tube to provide the necessary added mass for the wall.

Modifications may also be described, such as shown in Figs. 27 and 28, wherein the number of beads il are increased over that in the other modifications, Where six only are shown, there being eight in this particular modification. Since these beads, in conjunction with the exhaust tube, supply adequate mass to the stem base or wall, it has been found unnecessary to apply beads to the ends of the support wires B0. In the form of invention such as that shown in Figs. 21 to 26 inclusive, wherein beads are eliminated from one or more of the wires, it is understood that the wires have been appropriately coated with copper and a borate such as a copper berate in order 'to facilitate adherence oi the glass to the metal and prevent leakage.

In the description of the invention hereinabove made I have, for illustrative purposes, applied the same to a radio tube. However, it is obvious that the invention may be applied with equal facility to any other electric tube which requires an insulation base or stem such as glass to support electrical elements within an envelope. For example, a stem unit of this type may readily be applied to an electric lamp for supporting the lighting filament within the envelope. Similarly, the invention may be applied to X-ray tubes, rectifier tubes; and similar devices, or to glass tubes merely for sealing up an enlarged opening.

of the upper and lower plunger elements. In Fig. l

While glass is the obvious insulator employed in radio tubes and similar devices, it is apparent that other insulating viscous substances such as quartz could be employed as an envelope and stem material. I have also described the stem construction as being of tubular or cylindrical formation. However, for certain uses the stem section may take other forms.

It is desirable that the various wires forming the lead-in and support wires of the electrical device be placed in cylindrical formation, permitting the greatest displacement of one filament from another. This is of practical advantage in a radio tube, for example, where it is desirable that the inter-filament capacity be reduced as far as possible. This is accomplished in a circular arrangement of these wires, and in certain types of tubes the distance amounting to as high as 1000 inch, which is materially in excess of the distance ordinarily obtained in equivalent stem construction of the standard stem type, in these stems the distance ranging Ybetween 40/1000 to 60/1000 inch. This distance between the wires is increased over the direct distance by virtue of the fact that the contour of the stem wall is wavy or scalloped, thus securing the maximum surface separation between the wires. This surface distance between wires is not only of importance as regards inter-capacity efIects, but also as regards the development of electrolysis. Electrolysis arising from leakage between the lead-in wires causes a removal of the material of these wires and ulti- 1 gate leakage at the joints and destruction of the tube, and this difficulty is largely overcome by the relatively important increase in direct and surface distance between the various wires of the stem unit.

While I have shown the various wires in a circular arrangement to secure the maximum displacement one from another, it is, of course, obvious that other congurations depending upon the specific requirements of the electrical device may be made, such as square, oval or triangular arrangements.

A feature of the invention to which attention should be directed is the possibility of limiting the length of the lead-in wires inside of the tube, since by such limitation not only is the resistance of the lead-in circuit diminished, but the inductive eiects are also reduced. An outstanding advantage of the construction as describedv is that in eect the practical advantages of an all-metal tube are secured without the disadvantages. For example, the stem construction permits an extremely small size tube with a resultant diminution and reduction in undesired induction and resistance effects but without any increase of the inter-wire capacity effects. Further, by the utilization of an extended flattened stem head for the insertion of the various leadin and support wires the effective area for insertion of wires is practically doubled over that possible with the usual side-flattened press heretofore used in stern construction. For example, in comparable tube constructions in the stem of the prior art an over-all distance of about 3/4, inch is available, whereas in my stem construetion an over-all length of approximately 1% inches is made available.

A further noteworthy improvement over thc prior art as regards metal tubes resides in the elimination of diiilculties from gas occlusion which frequently arises in metals and which offers difficulty in the exhaust of the envelope.

The use of glass is based on improved methods developed over several decades of manufacture, and these improved methods are available .in the tube of my construction without sacrificing advantages as to size and the use of a metalshield.

enclosing the entire envelope.

lntha preferred modification of my invention wherein I utilize glass beads formed around the various wires oi.' the stem, an important advantage exists in that the glass does not 'necessarily require heating to a point where it flows readily or melts. It is necessary only that sufiicient heat be applied to the beads and adjacent stem wall and exhaust tube to secure a sufllcient plasticity to form a bridge between these elements. Avoidance of excessive heating reduces breakage in the final product. It hasbeen found that a difference of over 100 F. may exist between this plastic point of the glass and the increased temperature usually necessary to obtain a free flow of glass.

It is observed further that in the stem making machine the use of a rotatable head unit is not essential since satisfactory heating may be accomplished by stationary heating flames or jets.

It is apparent that modifications other thany those herein described may be made, provided such modifications are within'the scope of the claims hereto appended.

I claim as myy invention:

l. A stem assembly for electric tubes comprising a. short glass tube, a plurality of separate fusible elements forming a glass wall for one end of said tube, an exhaust tube passing through said wall, and a plurality of Wires sealed into said wall. l

2. A stem assembly for electric tubes comprising an open-ended fusible stem, a fusible beaded mass forming a wall at one end of said stem, said wall having a single( aperture therein, a readily fusible tube positioned within said stem and forming a connection with said aperture, and one or more wires sealed in said wall.

3. A stem assembly for electric tubes comprising a tubular open-ended stem, a mass of glass beads fused with each other and with one end of the stem interior to form a wall at said stem end,

and a plurality of wires sealed into said beads.v

4. A stem assembly for electric tubes comprising a tubular open-ended stem, a mass of glass beads fused with each other and with one end of the stem interior to form a wall at said stem end, a plurality of wires sealed into said beads, and an exhaust tube positioned within said stem and forming an opening through said wall.

5. A stem assembly for electric tubes comprising a stem, a wall forming a closure at one end of said stem, said wall consisting of a plurality of inter-fused and similar glass beads and a tubular member positioned within said stem.

6. The process of making a stem assembly which consists in placing within and adjacent an end of a tubular stem a plurality of wires embedded in glass beads and a centrally positioned exhaust tube, subjecting said stem end, beads and exhaust tube to progressive heating operations until the glass mass becomes viscous, forcing the exhaust tube axially toward the glass beads against a resistant element while preventing movement of the glass mass, and opening a gas passage from said exhaust tube through the glass mass.

7. An electric tube assembly comprising a glass envelope having an open end, a tubular glass stem sealed to said open end of the envelope, extending within said envelope, a plurality of similar ,glass beads forming a wall-across the inner end of said stem, and a plurality of wires. within said envelope, each of said wires being sealed by one of said beads.

8. An electric tube assembly comprising an envelope, a tubular glass stem sealed to and forming a part of the envelope, and extending within said envelope, a plurality of glass beads forminga glass wall closing the inner end' of said stem, and a plurality of circularly positioned electrical conductors positioned in said envelope, each of said conductors being sealed within one of the beads and extending within and without the envelope.

, 9. An electric tube assembly comprising an envelope, a tubular glass stem sealed to and forming a part of theV envelope and extending therein,

a plurality of glass beads forming a glass wall closing the inner end of said stem, a plurality of circularly positioned electrical conductors positioned in said envelope, each of said conductors being sealed within one of the beads and extending within and 'without the envelope, and an ex'- haust tube lying within the stem and opening into the envelope interior through said glass wall.

10. An electric tube assembly comprising an envelope, a tubular glass stem having a flared end sealed to said envelope and extending therein, a plurality of beads forming a wall closing the inner end of said stem, a plurality of circularly positioned electrical conductors positioned in said envelope, each of said conductors being sealed within one of the beads and extending within and Without the envelope, and an exhaust tube lying within the stem and opening into the envelope interior through said glass wall at a point within the area bounded by said conductors.

11. An assembly for electric tubes comprising an envelope, a tubular glass stem having a ared end sealed to said envelope and extending therein, a plurality of beads forming a wall closing the inner end of said stem, a plurality of circularly positioned electrical conductors positioned in said envelope, each of said conductors being sealed within one of the beads and extending within and without the envelope, an exhaust tube lying within the stem and opening into the envelope interior through said glass wall, a glass wall closing the inner end of said stem, a plurality of conductors arranged in circular formation embedded in said glass wall and extending within and without the envelope, said wall having an outlet aperture in the area bounded by said conductors.

l2. An electric tube construction comprising an envelope, a tubular stemv sealed to said envelope, a wall having undulating surfaces forming the closure to the inner end of said stem, a plurality of circularly disposed wires extending through said wall to the inside and outside of said envelope, and an exhaust tube opening to the envelope interior through said wall within the circular area defined by said Wires.

13. In an electric tube the combination of a glass envelope, a tubular glass stem having one end sealed to said envelope and extending therein, a plurality of lead-in wires circumferentially arranged within said stem, each of said wires being embedded within a glass bead at a point lying adjacent the inner end of the stem, a glass exhaust tube axially positioned within said stem, said exhaust tube and beads forming a fused glass wall sealing the inner end of said stem, a base support connected to said envelope and positioned at the stem end thereof ,`a plurality of contacts forming external connections to said wires, and an element assembly within said envelope and connected to said wires.

14. In an electric tube the combination of a glass envelope, a tubular stem having one end sealed to'said envelope and extending therein, a

plurality of lead-in wires circumferentially arranged within said stem, each of said wires being embedded within a glass bead at a point lying adjacent the inner end of the stem, an exhaust tube axially positioned within said stem, said exhaust tube and beads forming a fused glass wall sealing the inner end of said stem, a base support connected to said envelope and positioned at the stem end thereof, a plurality of contacts forming external connections to said wires, an element assembly within said envelope and connected to said wires, and an insulation plate interposed between said element assembly and stem.

15. An electric tube comprising an envelope having an open end, a stem tube sealed to said open end, a plurality of glass-like interfused beads forming a Wall closing the open end of the stem tube, and an electric conductor sealed in said wall, the identity of said beads being preserved in said wall.

16. A seal for an aperture bounded by rigid material comprising a plurality of interused glass beads in the aperture plane, said beads forming over one-half of said seal and retaining their identity after fusion.

17. A seal for an aperture bounded by rigid material comprising a plurality of interfused beadsand a wire positioned in one of said beads, said beads retaining their identity after fusion.

18. A seal for an aperture bounded by vitreous material 'comprising a plurality of interfused beads and two concentric tubes, said beads forming an annular bridge between adjacent tube ends.

19. A seal for an aperture bounded by vitreous material comprising a plurality of interfused beads and two concentric tubes, said beads forming an annular bridge between adjacent tube ends, the inner annular section of the bridge being thinner than the outer section.

20. A seal for an aperture bounded by vitreous material comprising a .plurality of interiused.

beads and two concentric tubes, said beads forming an annular bridge between adjacent ltube ends, and a plurality said bridge. i

21. The process of making a closure for an exhaust tube which comprises placing within and adjacent the end of a tubular stem a plurality of conductors, a centrally positioned exhaust tube, and a glass mass intermediate the exhaust tube and the stem, subjecting said stem end, exhaust tube and glass mass to heating operations until the glass becomes viscous, applying pressure against the viscous glass mass whereby a bridging wall is formed between the exhaust tube and the stem wall, and opening a gas passage through said exhaust tube.

22. A process of forming a glass seal'for an aperture bounded by vitreous material which comprises the steps of positioning glass beads in the aperture plane, heating said beads to the plastic stage, applying pressure to the beads normally to the aperture plane to bring about coalescence of the beads and of the beads and aperture edge.

23. A process of forming a seal for an aperture having a rigid edge which comprises the steps of positioning glass masses within the apertures, heating the masses to the plastic point, applying pressure to the masses in a direction normal to the aperture plane causing transverse movement thereof toward said rigid aperture edge, whereby the masses are coalesced and forced into close adherence with said aperture edge.

24. A stem assembly I or electric tubes comprising an open ended tube, a plurality of discrete glass-like beads forming a wall closing an open end of said tube, and a conductor sealed in said wall, said beads showing their original conformation in and forming over ilfty percent oi said wall.

CLARENCE A. HORN.

of wires passing throughv 

